nodejs access main script context

Question

Diving into node, I have a question on how an included script, can access the main's script methods or variables

For instance, say that I have a logger object initiated in the main script and I include another js file, which needs access to the logger. How can I do that, without injecting the logger to the included script.

//main node script

var logger = require('logger'),
    app = require("./app.js")

//app.js

function something(){
  //access logger here !!!!!!!
}

exports.something = something

Hope it is clear

Thanks

David Oliveros · Accepted Answer · 2013-09-25 15:06:48Z

3

Try doing:

//main node script

var logger = require('logger'),
    app = require("./app.js")(logger);

//app.js

var something = function (logger){
  logger.log('Im here!');
}

module.exports = exports = something;

Edit:

If you want to split your main app's code into different files, on your main script file you can do something like: (This is how I'm splitting my main app.js into different sections)

// main app.js

express = require('express');
...

/* Routes ---------------------*/
require('./config/routes')(app);

/* Socket IO init -------------*/
require('./app/controllers/socket.io')(io);

/* Your other file ------------*/
require('./path/to/file')(app);
...


// config/routes.js

module.exports = function(app){

    app.configure(function(){
        app.get('/', ...);
        ...
    }
}


// app/controllers/socket.io.js

module.exports = function(io){
  // My custom socket IO implementation here
}

// ...etc

Edit 2:

Your function can also return a JS object, in case you want to do something on the main app.js with a custom script.

Example:

// main app.js

...

/* Some controller ---------------------*/
var myThing = require('./some/controller')(app);

myThing.myFunction2('lorem'); // will print 'lorem' on console
...


// some/controller.js
// Your function can also return a JS object, in case you want to do something on the main app.js with this require 

var helperModule = require('helperModule');

module.exports = function(app){

  var myFunction = function(){ console.log('lorem'); }

  // An example to export a different function based on something
  if (app.something == helperModule.something){
    myFunction = function() { console.log('dolor'); }  
  }

  return {
    myFunction: myFunction,
    myFunction2: function(something){
      console.log(something);
    }
  }
}

You can also simply export a function or an object containing functions, without sending any parameter like this:

// main app.js

...
var myModule = require('./path/to/module');
myModule.myFunction('lorem'); // will print "lorem" in console
...


// path/to/module.js

module.exports = {
  myFunction: function(message){ console.log(message); },
  myFunction2: ...
}

Basically, whatever you put inside module.exports is what gets returned after the require() function.

edited Sep 25, 2013 at 15:06

answered Sep 25, 2013 at 14:11

David Oliveros

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4 Comments

Thomas Over a year ago

Thanks. No way without injecting the dependency? It can become messy if you need to access several modules

David Oliveros Over a year ago

You have to manually send the objects that you wish to keep consistent on the splitted files (Like the app object), but you can also call var myModule = require('myModule') on the include files without calling them on the main app.js script. That way, you can only require the modules that will be used on each splitted file.

Thomas Over a year ago

Thanks. Can you elaborate on the module.exports = function().. statement? I understand that this way you can configure the service. But if you also want to expose a method of the included script, to the main, how would that be done?

David Oliveros Over a year ago

Sure. *Look at Edit 2

Plato · Accepted Answer · 2013-09-25 15:08:41Z

module.exports is what is returned when you require the file. in @DavidOliveros example, that's a function that takes app or io as parameters. the function is executed right after the require takes place.

If you want to expose a method of the included script to the main, try this:

// child.js
module.exports = function(app){
  var child = {};
  child.crazyFunction = function(callback){
    app.explode(function(){
      callback();
    });
  };

  child.otherFunction = function(){};
  return child;
};

// app.js
var express = require('express');
var app = module.exports = express();
var child = require('./child.js')(app);
app.get('/', function(req, res){
  child.crazyFunction(function(){
    res.send(500);
  });
});

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